Showing papers by "Y.Y. Lau published in 2011"

Contact Resistance with Dissimilar Materials: Bulk Contacts and Thin Film Contacts

Abstract: Contact resistance is important to integrated circuits and thin film devices, carbon nanotube based cathodes and interconnects, field emitters, wire-array z-pinches, metal-insulator-vacuum junctions, and high power microwave sources, etc. In other applications, the electrical contacts are formed by thin film structures of a few microns thickness, such as in micro-electromechanical system (MEMS) relays and microconnector systems. This paper summarizes the recent modeling efforts at the University of Michigan, addressing the effect of dissimilar materials and of finite dimensions on the contact resistance of both bulk contacts and thin film contacts. The Cartesian and cylindrical geometries are analyzed. Accurate analytical scaling laws are constructed for the contact resistance of both bulk contacts and thin film contacts over a large range of aspect ratios and resistivity ratios. These were validated against known limiting cases and spot-checks with numerical simulations.

Recirculating planar magnetrons: Simulations and experiment

Abstract: The Recirculating Planar Magnetron (RPM) is a crossed-field device which presents numerous advantages in generating HPM. A 12-cavity, conventional-polarity, 1GHz model was designed and tested at a −300 kV, 0.3–0.5 microsecond pulselength and a 0.3 T axial magnetic field. The initial design and experimental results are discussed.

Recirculating Planar Magnetron modeling and experiments

Abstract: The Recirculating Planar Magnetron (RPM) [1] is a new class of crossed-field device that combines the advantages of high-efficiency recirculating devices with those of planar devices: both large-area cathode (high current) and anode (improved thermal management). Two embodiments of the RPM are modeled and under design: 1) Axial magnetic field with radial electric field (Fig. 1) and 2) Radial magnetic field and axial electric field (Fig.2)

Plasma instability measurements on planar Al foil loads driven using the MAIZE 1-MA LTD facility

Abstract: Initial dynamic load experiments were performed on UM's 1-MA linear transformer driver (LTD) facility, MAIZE, to characterize magneto-Rayleigh-Taylor (MRT) instability growth and plasma dynamics on planar-foil plasmas. The MAIZE LTD is capable of delivering a 1-MA, < 100 ns risetime drive pulse into a 0.1 Ω matched load with a ±100 kV charge. For these dynamic load experiments the LTD was charged to ±70 kV to deliver up to 0.7 MA with a 170 ns risetime into the foil load.

Some unusual properties of the cylindrical Brillouin flow

Abstract: It was recently found that the Buneman-Hartree (B-H) condition in a cylindrical relativistic magnetron assumes a very different form depending on the single particle model or the Brillouin flow model [1]. Such a difference is always present, whether the voltage is relativistic or not. These two models yield the same result only in the limit of a planar magnetron. As the difference between the conventional and the inverted magnetron arises only in a cylindrical geometry, the cylindrical Brillouin flow is of renewed interest because the inverted magnetron exhibits the negative mass instability [2], which is utilized in our recent invention of the recirculating planar magnetron [3,4]. We find that there is yet another novel property of the cylindrical Brillouin flow. If we replace the gap voltage by the spatially varying scalar potential, and the magnetic field by the spatially varying vector potential, both the B-H condition and the Hull cutoff condition are satisfied at all radii within the cylindrical Brillouin flow if the phase velocity of the wave in the B-H condition is replaced by the local electron flow velocity. This property does not seem to have been noted previously, and its implications are being explored. The negative mass effects in the Brillouin flow in the inverted magnetron configuration, as well as the role played by the slow wave structure at the anode, will also be studied.

An exact formulation of thin film contact resistance with dissimilar materials

Abstract: Summary form only given. Thin film contact is a very important issue in many areas, such as integrated circuits, thin film devices, carbon nanotube and carbon nanofiber based cathodes and interconnects, field emitters, etc. In high energy density physics, the electrical contacts between the electrode plates and in Z-pinch wire arrays are crucial for high current delivery. This paper presents results of thin film contact resistance with dissimilar materials, based on an exact analytic formulation of a model for both cylindrical and Cartesian geometry. In the cylindrical geometry, the model consists of a long cylindrical rod of radius a standing on the center of large thin-film circular disk of thickness h, and radius b (>; a). The rod's electrical resistivity and the thin film's electrical resistivity may have an arbitrary ratio. We found that, over a large range of parameters, the contact resistance does not depend on b as long as either b >;>; a or b >;>; h. We also found that the contact resistance is insensitive to the resistivity ratio for a/h ; 1. Our calculations are verified in various known limits. We obtained the condition under which the thin film contact resistance is minimized, for arbitrary resistivity ratio. Electric field patterns will also be presented that show crowding of the field lines in the contact region for h >;>; a and for a >;>; h. The contact resistance for the Cartesian thin-film geometry will be presented. Our theory was validated against MAXWELL 3D simulation, and against conformal mapping results for unity resistivity ratio. Optimal conditions to minimize the thin film contact resistance are identified.